html-display-nesting-width: preference variable

Default value: 40

In HTML and XML modes, the mode line displays the names of the
innermost tags in effect at the start of the current line. This
variable controls how much space is allocated for that display.
Smaller values let Epsilon use more of the mode line for tag names, so
the buffer's file name is more likely to be abbreviated. You can use
the html-list-element-nesting command to display all the tags.